Q. I am having some problems with my plants that I can't figure out, but wonder if it has something to do with a lack of phosphorus. They are in a 32-gallon tank I set up seven weeks ago. Three plants — Eusteralis stellata, Rotala wallichii and Ludwigia arcuata — are not growing well. The newer leaves are coming in increasingly smaller, and the tops of the stems are dying.
I had this problem before with the Eusteralis in another tank, with the new stems growing from the sides of the dying tops. Some leaf edges roll up into the leaf, and in extreme cases they create a tube out of the entire leaf. The Ludwigia arcuata has twisted smaller leaves on the top. The other plants in the tank are growing without problems — E. schlueteri, Didiplis diandra, Rotala macrandra, Glossostigma, Echinodorus tenellus, Limnophila aquatica, Lilaeopsis (New Zealand grass), Micranthemum micranthemoides, M. umbrosum, Nesaea sp., N. crassicaulis, Ammannia senegalenis, hairgrass and Barclaya longifolia.
There is sufficient CO2, good light, a reasonable fish load and I feed modestly. The substrate has very little peat, and I add Tetra cryptotabs, NPK fertilizer (just a bit) and Ferrotabs. Water changes are done every four or five days — 5 to 15 percent — with Tropica Master Grow or Duplaplant 24. The temperature is always 75 degrees Fahrenheit, pH is 7.0, KH is 10, GH is 12 and nitrate is about 10 parts per million or less. The lights are on for 13 hours a day, with a 1½-hour interruption at midday.
As a result of the problems noted above, I have used several other fertilizers, which has brought improvement (especially to the Eusteralis), but not a complete cure. What could be wrong?
The authors of one plant book noted that when the phosphate level went from 0.7 0.1 the leaves wrapped as mine are doing. Perhaps, despite the 20 fish in the tank, the phosphate, ammonium, calcium and so on are now minimal.
A. I would be extremely surprised if your problem is a macronutrient (NPK) deficiency, for a couple of reasons. First, plants are very good at scavenging even minute quantities of these minerals from the environment, and with fish in the tank that are being fed regularly, there is usually plenty of nitrogen (N) and phosphorus (P) available. Under certain circumstances, a tank can become potassium (K) deficient if you are depending only on fish wastes for plant nutrition. But most good aquatic plant fertilizers contain potassium for exactly this reason. The products you are using should supply this mineral adequately.
The clue that makes me most sure that phosphate deficiency is not the problem here is that with this nutrient you should see problems first in older foliage rather than the growth shoots. This sounds very similar to a problem I had earlier this year. I was pretty sure in my case that it was not a deficiency I was seeing, but a toxicity problem. I had set the tank up with quite a rich soil-based substrate. Some of the plants, Echinodorus spp. in particular, did very well right from the beginning. The stem plants took a serious hit. It took several months, some big water changes and a long session of gravel vacuuming large sections of the substrate (concentrating on the areas around the plants most affected) before things turned around.
This is one of the things that makes tracking down specific problems so difficult. Sometimes we are seeing deficiencies, sometimes we are seeing toxicity, and, sometimes, an overabundance of one mineral can block the uptake of others.
Troubleshooting problems like this can be trying. If some of the plants are showing good, normal growth (as most of yours seem to be), I suspect it is not a nutrient deficiency, but some specific conditions that bother one (or a few) particular species. We sometimes forget that our goal in a planted tank is usually to maintain conditions that will support as many species as possible. The fact is, however, that all species of plants do not have exactly the same requirements. We have to accept that we will not always be able to grow every type of plant in the same tank, just as we choose fish for a community tank based on similar environmental requirements.
If you really want to grow the plants you are having trouble with, I would isolate them in another tank and work on providing for just their needs. When you have learned what — with your specific water conditions — you need to do to grow those species, you can plan a plant community around them. In all probability, though, you will find that there are other species that will not thrive under this new set of conditions.
Dark Algae
Q. I am having a problem with dark green, skin-like algae in my 75-gallon tank. It's everywhere, and while it's easy enough to strip off sheets of it by hand or with the siphon, it's so time consuming — and it's all back anyway within a couple of days. Do you have a solution to the problem? I'd be very interested in hearing what works.
This is a relatively new tank, a community display. When it was first set up, prior to fish being introduced, I went on vacation for four days and decided it was probably better to leave the lights on rather than off. There is also some crushed sea grit added to the gravel, and I can't get the pH down below 7.6 no matter what I do.
A. The type of "algae" you describe is actually a cyanobacteria or blue-green algae. It is also characterized by a very distinctive woodsy odor. It can, indeed, be a very frustrating problem. It's almost always brought on by high nutrient levels in the tank, and can usually be brought under control by reversing this situation.
The first course of action should be to do a series of large, closely spaced water changes. I suggest 50 percent daily for a week or so. At the same time, manually remove as much cyanobacteria as you can.
Re-assess the stocking levels in the tank, and make sure you are not pushing the limits. At the same time, look at your feeding routine and make sure you're not overfeeding. Also make sure you are not using any products that could introduce phosphate and nitrate into the system. Besides poorly designed aquatic fertilizers and most terrestrial fertilizers, many pH-adjusting products and even some water conditioners contain phosphate.
Be extra diligent about removing older leaves before they have a chance to decay and release nutrients back into the system. It can also help to put a sponge prefilter on your filter intakes. Rinse this prefilter no less often than every two days so that the solid material collected has not chance to be broken down into the water.
If your town introduces phosphate to your tap water in order to coat the pipes, the phosphate levels can be a real nuisance. You may find it helpful in these instances to use a phosphate removing resin in your filter.
With all the above measures, you should see the cyanobacteria start to die back in a period of weeks. But remember, it is likely to reoccur if maintenance again begins to slip.
If you've done all the clean up, but are unwilling to wait it out, cyanobacteria can be killed with erythromycin (brand name Maracyn, among others). I have used the dose suggested on the package, but treating for 24 or at most 48 hours is usually enough to kill blue-green algae. Erythromycin can suppress the biological filtration in the tank, so be prepared to step in with heavy water changes if you find ammonia levels increasing.
Leaving the lights on 24 hours a day while you were away was not a good idea. Most of the plants we use in the aquarium come from tropical areas, and are adapted to about 10 and 14 hours each of day and night. At 2 to 3 watts per gallon of fluorescent light, a 12-hour photoperiod works well for me. This can be adjusted based on lighting intensity. In no case does it make sense to extend the photoperiod much beyond 14 hours. Most higher plants will stop photosynthesizing at this point, while the algae will take full advantage of this situation.
The high pH is directly related to the calcium releasing nature of the substrate. Although you could still have lowered the pH adequately with supplemental CO2, it probably would not have gotten rid of the cyanobacteria.
Tearing down a tank to solve an algae problem is the last resort, and unless tank management changes, the algae will likely return. However, stripping the aquarium can quickly solve whatever high nutrient problems you have in the tank.